1. Field of the Invention
This invention relates to a device for measuring adhesive strength and shear strength of coated film, which makes quantitative measurement of the adhesive strength and shear strength of a film coated on an object so as to find out the basic properties of the film thus coated.
2. Discussion of Background
A conventional device for measuring adhesive strength of a coated film is as disclosed in, for example, Japanese Patent Application No. 178759/1986 invented by the present inventors and titled "Device for Measuring Adhesive Strength of Coated Film", the structure of which is as shown in FIG. 12 of the accompanying drawing.
In the drawing, a specimen mounting base (34) is fixed onto a sliding member (33) which is pivotally mounted on a guide shaft (32) immovably fastened to a support stand (31). A coated plate (35) to be a test specimen is mounted onto this specimen mounting base (34) by means of a specimen fixing implement (36). A screw-threaded rod (38) is screw-engaged in a nut (37) coupled to the specimen mounting base (34), one end part of which is connected with a motor (39). The sliding member (33) can be displaced linearly in the horizontal direction along the guide shaft (32), and slidingly moves on and along a guide shaft (41) fixed on the support stand (31) through a connecting member (40). The connecting member (43) fixed on the sliding member (42) is connected with another connecting member (45) fixed on another sliding member (44), whereby a guide shaft (46) causes the sliding member (44) to slide up and down. One end part of the guide shaft (46) constitutes a supporting body for a cutting blade (47), while the other end part thereof forms a screw-threaded rod where a thumb nut (48) for holding the cutting blade and a weight (49) are disposed. The weight (49) functions to adjust and establish the press-contacting force of the cutting blade (47) to the film coated plate (35). The front end part of a micrometer (50) fixed to the connecting member 45) is urged to the other connecting member (43) in a manner to cause the front end part of the cutting blade (47) to be in parallel with the surface of the material as the test specimen.
A pressure detector (51) fixed on the connecting member (40) detects a repulsive force to be generated against the cutting blade (47) through the sliding member (42) and the connecting rod (52). Measured data are converted by means of an A/D converter (53), then the A/D-converted data are introduced as inputs into a personal computer (54) wherein they are subjected to waveform-processing with use of a Fourier transformation program, and finally the thus waveform-processed data are outputted in the form of Fourier spectra, power spectra, and a graph of self-correlation function. A temperature regulator (55) such as a thermo-module is used for adjusting a temperature of the test specimen.
A coated plate having, for example, a length of 150 mm, a width of 70 mm, and a thickness of 1 mm was used as the test specimen (35) and a part of the coated film was peeled off in a size of 2 cm square to expose the surface of the base material. This partially exposed coated plate (35) was mounted on the specimen mounting base (34) by means of the specimen fixing implement (36) in such a manner that it may be tightly attached to the base, and then the cutting blade (47) having a blade width of 4 mm was applied onto the exposed part of the coated plate (35) and pushed against the coated plate by means of the weight (49) so that a pressing force of 600 g may be exerted to it. Then, adjustment is made by a micrometer (50) to bring the edge of the cutting blade (47) to be in parallel with the surface of the test specimen.
Then, an electric motor is driven to shift the coated plate (35) at a velocity of 1 mm/min., while detecting by means of the pressure detector (51) an interfacial cutting resistance to the cutting blade (47) which has been transmitted to it through the connecting rod (52) fixed to the sliding member (42). First of all, a part of the base material is cut in 5 mm length, followed by cutting a part of the coated film in 15 mm length. Then, by use of the thermo-module (55), the temperature of the coated plate is regulated to a constant temperature level ranging from -10.degree. C. to 60.degree. C.
FIG. 13 of the accompanying drawing is a characteristic diagram showing the cutting resistance to the cutting blade at the interface between the base material and the coated film, wherein the ordinate axis denotes the cutting resistance (kg) at an interface between the coated layer and the base material, and the abscissa axis represents a cutting length (mm) of the interface between the coated film and the base material. As seen from this characteristic diagram, the measured data appear in the waveform, in which "A" indicates the cutting resistance of the surface of the base material, and "B" indicates the cutting resistance of the interface between the coated film and the base material.
FIGS. 14(a), 14(b) and 14(c) are graphical representations corresponding to FIG. 13 above, respectively showing the cutting resistance at the interface in case the conditions for the surface treatment of the base material are varied for coating an epoxy type film by electrical deposition, in which FIG. 14(a) is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the surface preparation of the base material with use of zinc phosphate in acicular crystal; FIG. 14(b) is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the surface preparation of the base material with use of zinc phosphate in columnar crystal; and FIG. 14(c) is the characteristic diagram of the interfacial cutting resistance of the test specimen which has been subjected to the surface preparation of the base material with use of zinc phosphate in scaly crystal. It will be seen from these characteristic diagrams that, even when the coated film is of the same material, if the formation treatment of the treated steel plate differs, the adhesive strength of the coated film differs accordingly with the consequence that the interfacial cutting resistance and the waveform become varied, as shown in FIGS. 14(a), 14(b) and 14(c).
FIG. 15 is a flow chart for the wave form analysis program, in which the measured data (55) of the interfacial cutting resistance is processed by the A/D converter (56), inputted into the personal computer (57), and outputted to a program file (58). After producing the output data of the program file (58) in the form of a graph, a processing range is inputted by a cursor from the image plane, followed by processing (60) the measured data by use of the subsequent Fourier conversion program (59) to output the result of conversion into the file.
Then, the inputs are introduced into the respective files of Fourier spectra, power spectra and self-correlation function, from which graphs are outputted (61).
FIG. 16 is a power spectral diagram to be obtained by the Fourier conversion of the interfacial cutting resistance of a urethane type coating material for each heating time of zero hr., 100 hrs., 300 hrs., and 650 hrs.. In this graphical representation, the abscissa represents the number of vibration (cps) and the ordinate denotes power spectrum (cm.sup.2 /sec.sup.3). From this graph, it will be seen that, in the heat-resistance test at 160.degree. C., the power spectrum tends to lower while the peak number of vibration tends to increase as the heating time becomes prolonged.
The interfacial cutting resistance is a composite force of the adhesive strength of the coated film and the material strength, the breaking form of which is recorded as a waveform. By subjecting the measured values of the interfacial cutting resistance to the Fourier conversion and then carrying out the waveform analysis, there can be obtained information for clarifying the nature of the phenomenon.
By the way, in the above-described conventional device for measuring the adhesive strength of the coated film, explanations have been made as to an instance of using a general coated plate having a film thickness of a few tens of micrometers or above. It may, however, be feasible that film be coated on a plastic plate to obtain the same effect as in the above-mentioned conventional example.
On account of such construction of the conventional device for measuring the adhesive strength of the coated film as described above, it was necessary to provide the coated plate (35) for the film testing purpose and to analogize the adhesive strength of the coated film of the object to be tested on the basis of this result of measurement, hence there remained problems in respect of reliability and precision of the result of measurement (or analogy).
There was also a problem such that the conventional device is able to find out variations in the adhesive strength of the coated film only indirectly by the waveform analysis due to the cutting force and the Fourier conversion from the resulted waveform, and no adhesive strength and the shear strength can be found out directly.